THE DIAGNOSTICS OF THE FERMI@ELETTRA BUNCH COMPRESSORS

Bunch compressors (BC) are key components of the seeded FEL FERMI@ELETTRA. A complete set up of non destructive diagnostics is foreseen to provide the required stability for the production of sub-psec electron bunches. Main task of these diagnostics is to provide the error signals to the feedback systems used to stabilize the energy and the peak current of the electron bunch which are crucial parameters for optimum FEL operation. The different operation regimes foreseen for FERMI [1] call for a flexible set-up, for both the bunch compressors and the associated diagnostics. In this paper we present the adopted diagnostics for the measurement of position, energy and energy spread; both “energy” BPM, in between bunch compressors (BC), and optical transition radiation (OTR) screen plus wire scanner have been adopted. The design of a relative bunch length monitor needed for the determination of the optimal compression and for peak current stabilization is presented as well. The scheme is based on non-invasive techniques, namely the detection of the coherent synchrotron radiation (CSR) from the last bending of the BC plus the coherent diffraction radiation (CDR) from a downstream slit. Finally, a technique for the bunch phase measurement is presented.